The present invention relates to a fuel cell generation system and particularly relates to a fuel cell generation system for reforming a material fuel to obtain a reformed gas having a high hydrogen content, i.e. hydrogen rich, supplying the reformed gas and oxygen containing gas to a fuel cell in which the reformed gas and oxygen containing gas are reacted to each other to thereby generate power.
Japanese Patent Application Laid-Open publication No. 5-036429 discloses a fuel cell generation system including a reforming apparatus for reforming material fuel gas and manufacturing reformed gas having a high hydrogen content and causing the obtained reformed gas to react to oxygen containing gas supplied separately to thereby generate power.
This fuel cell generation system controls and regulates the flow rate of the material fuel introduced into the reforming apparatus in accordance with the variation of load power required by an external load.
If the power requirement from the external load rapidly increases and the generation of the reformed gas supplied from the reforming apparatus cannot follow up the requirement due to the large increase of the requirement, the excess current-carrying to a pseudo-load arranged in advance in addition to the external load is reduced so as to satisfy the required power supply.
According to the studies done by the inventors of the present invention, however, the conventional fuel cell generation system has disadvantages such that it is not sufficiently taken into consideration to maintain operating pressures of both a reforming apparatus for reforming a material fuel and a fuel cell for causing a reaction between a reformed gas and an oxygen containing gas to thereby generate power. This makes it difficult to maintain the operating pressures in an appropriate manner.
Namely, if the flow rate of the material fuel is varied in accordance with the variation of the external load, the quantity of a reformed gas generated by the reforming apparatus is varied, as well. The variation of the quantity of the reformed gas thus generated causes that of the internal pressure of the reforming apparatus.
Nevertheless, due to the fact that the appropriate maintenance of the operating pressure within the reforming apparatus is not sufficiently taken account of in the conventional system, there is a possibility that the internal pressure of the reforming apparatus reaches the upper or lower operating pressure limit.
If the quantity of the reformed gas generated in the reforming apparatus varies according to the variation of the flow rate of the material fuel, then the quantity of the reformed gas supplied to the fuel cell is also varied, which variation, in turn, causes the variation of the internal pressure of the fuel cell.
Here again, due to the fact that the appropriate maintenance of the operating pressure within the fuel cell is not sufficiently taken account of, there is a possibility that the internal pressure of the fuel cell reaches the upper or lower operating pressure limit.
Furthermore, in both of the reforming apparatus and the fuel cell, it is required to operate them while changing the target appropriate operating pressures according to the variation of an external load, respectively. Besides, it is required to change the upper and lower operating pressure limits of the operating pressures according to the variation of the external load, respectively.
As can be seen from the above, if the upper and lower limits of the operating pressures of the reforming apparatus and the fuel cell vary according to the variation of the external load, respectively and the target operating pressures of the reforming apparatus and the fuel cell vary according to the variation of the external load, respectively, then it may be very difficult to maintain the target appropriate operating pressures of the reforming apparatus and the fuel cell, respectively.
Judging from the above, according to the conventional fuel cell generation system, there is a possibility the balance between the pressure of the reforming apparatus and that of the fuel cell is difficult to keep appropriately and, therefore, the operation of the overall fuel cell generation system cannot continue well.
Aside from the above studies, the fuel cell is constructed to generate power as a result of the reaction between the supplied reformed gas and the oxygen containing gas. Due to this, the load power which can be taken out from the fuel cell depends on the quantity of the supplied reformed gas and that of the supplied oxygen containing gas.
Among these gases, the oxygen containing gas is not supplied by generating an oxygen gas through a chemical reaction but supplied as air from an external air supply unit. Thus, the supply quantity of the oxygen containing gas can be controlled easily as required.
On the other hand, the reformed gas is generated by the reforming apparatus. Owing to this, the chemical reaction of the reformed gas causes a time delay and the quantity of the generated reformed gas is difficult to determine in an accurate manner.
In this way, the power generation in the fuel cell mainly depends on the supply quantity of the reformed gas. Thus the load power which can be taken out from the fuel cell mainly depend on the quantity of the reformed gas supplied to the fuel cell.
According to the conventional fuel cell generation system, however, the actual load power taken out from the fuel cell is not set in view of the quantity of reformed gas supplied to the fuel cell. There is a possibility, therefore, that if the load power which quantity exceeds the original supply limit of the load power is taken out from the fuel battery, the fuel cell is disadvantageously damaged.
The present invention has been made through the above-stated studies. It is, therefore, an object of the present invention to provide a fuel cell generation system capable of individually operating a reforming apparatus and a fuel cell at their intended operating pressures, generating power while appropriately maintaining the pressure balance between the reforming apparatus and the fuel cell and effectively preventing the load power exceeding the capability of the fuel cell from being taken out from the fuel cell.
A fuel cell generation system according to the present invention comprises a reforming apparatus reforming material fuel and generating reformed gas that is hydrogen rich; a fuel cell causing a reaction between oxygen containing gas and the reformed gas supplied from the reforming apparatus and generating power; a reformed gas flow rate control section controlling a flow rate of the reformed gas flowing from the reforming apparatus so that an operating pressure of the reforming apparatus is equal to a target pressure thereof; a reformed gas flow rate detecting section detecting a flow rate of the reformed gas flowing into the fuel cell; a target load current calculating section calculating a target load current taken out of the fuel cell in accordance with the flow rate of the reformed gas detected by the reformed gas flow rate detecting section so that the operating pressure of the fuel cell is equal to a target pressure thereof; an inlet pressure detecting section detecting an inlet pressure of the fuel cell; a target load current correction quantity calculating section calculating a load current correction quantity in accordance with a deviation between the inlet pressure of the fuel cell detected by the inlet pressure detecting section and the target pressure of the fuel cell; and a correction quantity adding section adding the target load current calculated by the target load current calculating section and the load current correction quantity calculated by the target load current correction quantity calculating section.
With this configuration, it is possible to operate the reforming apparatus and the fuel cell without carrying a load current exceeding the capability of the fuel cell and while keeping the pressure balance between the reforming apparatus and the fuel cell and maintaining the operating pressures of both the reforming apparatus and the fuel cell to their respective target operating pressures.
In other words, a fuel cell generation system according to the present invention comprises a reforming apparatus reforming material fuel and generating reformed gas that is hydrogen rich; a fuel cell causing a reaction between oxygen containing gas and the reformed gas supplied from the reforming apparatus and generating power; reformed gas flow rate control means for controlling a flow rate of the reformed gas flowing from the reforming apparatus so that an operating pressure of the reforming apparatus is equal to a target pressure thereof; reformed gas flow rate detecting means for detecting a flow rate of the reformed gas flowing into the fuel cell; target load current calculating means for calculating a target load current taken out of the fuel cell in accordance with the flow rate of the reformed gas detected by the reformed gas flow rate detecting means so that the operating pressure of the fuel cell is equal to a target pressure thereof; inlet pressure detecting means for detecting an inlet pressure of the fuel cell; and target load current correcting means for calculating a load current correction quantity in accordance with a deviation between the inlet pressure of the fuel cell detected by the inlet pressure detecting means and the target pressure of the fuel cell and for adding the target load current calculated by the target load current calculating means and the load current correction quantity.